If within a company system, e.g. a company email mail box system and addresses, then of course. It has the same restrictions as verbal. To exclaim an email on a company system is confidential does have confidentiality up to the extent of policy and the law. Citing City of Ontario v. Quon (2010) the courts state the place of business can seize and search and/or monitor and etc. company owned communication systems.
Therefore, if an email is sent, a text message, or even a phone call with a company phone cell or land line the company has rights and can access that communication. Remember in a corporate world the corporation is an entity employing individuals and managed by individuals, yet again is an entity defined by words on paper and laws.
Has the familiar company policy of no cell phone usage on company property or during work hours not been pondered. Those are subject to conflicting legal views, but generally are subject to federal search and seizure laws requiring a warrant.
Anything communicated is subject by confidentiality first by those two or more parties, where, and how the communication occurs. Ponder the most recent discussions with the NSA and email monitoring in our U.S. Congress.
Insert common legal disclaimer here in regard to legal advice and etc.